diff --git a/toxcore/Lossless_UDP.c b/toxcore/Lossless_UDP.c
index bdf5cd4c..0d859435 100644
--- a/toxcore/Lossless_UDP.c
+++ b/toxcore/Lossless_UDP.c
@@ -548,6 +548,30 @@ int discard_packet(Lossless_UDP *ludp, int connection_id)
 }
 
 #define MAX_SYNC_RATE 20
+#define MIN_SLOTS 16
+/* returns the number of packet slots left in the sendbuffer.
+ * return 0 if failure.
+ */
+uint32_t num_free_sendqueue_slots(Lossless_UDP *ludp, int connection_id)
+{
+    if ((unsigned int)connection_id >= ludp->connections.len)
+        return 0;
+
+    Connection *connection = &tox_array_get(&ludp->connections, connection_id, Connection);
+    uint32_t max_slots = (connection->data_rate / MAX_SYNC_RATE) * 1.5;
+
+    if (max_slots > MAX_QUEUE_NUM)
+        max_slots = MAX_QUEUE_NUM;
+
+    if (max_slots < MIN_SLOTS)
+        max_slots = MIN_SLOTS;
+
+    if (sendqueue(ludp, connection_id) > max_slots)
+        return 0;
+
+    return max_slots - sendqueue(ludp, connection_id);
+}
+
 
 /*  return 0 if data could not be put in packet queue.
  *  return 1 if data was put into the queue.
@@ -565,9 +589,10 @@ int write_packet(Lossless_UDP *ludp, int connection_id, uint8_t *data, uint32_t
     if (length > MAX_DATA_SIZE || length == 0 || sendqueue(ludp, connection_id) >= MAX_QUEUE_NUM)
         return 0;
 
+    if (num_free_sendqueue_slots(ludp, connection_id) == 0)
+        return 0;
+
     if (sendqueue(ludp, connection_id) >= connection->sendbuffer_length && connection->sendbuffer_length != 0) {
-        if (sendqueue(ludp, connection_id) > connection->data_rate/MAX_SYNC_RATE)
-            return 0;
         uint32_t newlen = connection->sendbuffer_length = resize_queue(&connection->sendbuffer, connection->sendbuffer_length,
                           connection->sendbuffer_length * 2, connection->successful_sent, connection->sendbuff_packetnum);
 
@@ -578,7 +603,6 @@ int write_packet(Lossless_UDP *ludp, int connection_id, uint8_t *data, uint32_t
         return write_packet(ludp, connection_id, data, length);
     }
 
-
     uint32_t index = connection->sendbuff_packetnum % connection->sendbuffer_length;
     memcpy(connection->sendbuffer[index].data, data, length);
     connection->sendbuffer[index].size = length;
diff --git a/toxcore/Lossless_UDP.h b/toxcore/Lossless_UDP.h
index 8a1c9c53..3d782be7 100644
--- a/toxcore/Lossless_UDP.h
+++ b/toxcore/Lossless_UDP.h
@@ -217,6 +217,11 @@ int read_packet_silent(Lossless_UDP *ludp, int connection_id, uint8_t *data);
  */
 int discard_packet(Lossless_UDP *ludp, int connection_id);
 
+/* returns the number of packet slots left in the sendbuffer.
+ * return 0 if failure.
+ */
+uint32_t num_free_sendqueue_slots(Lossless_UDP *ludp, int connection_id);
+
 /*  return 0 if data could not be put in packet queue.
  *  return 1 if data was put into the queue.
  */
diff --git a/toxcore/Messenger.c b/toxcore/Messenger.c
index 60fcc0ba..5ed94bb7 100644
--- a/toxcore/Messenger.c
+++ b/toxcore/Messenger.c
@@ -1091,7 +1091,7 @@ int file_control(Messenger *m, int friendnumber, uint8_t send_receive, uint8_t f
     }
 }
 
-
+#define MIN_SLOTS_FREE 4
 /* Send file data.
  *
  *  return 1 on success
@@ -1108,6 +1108,10 @@ int file_data(Messenger *m, int friendnumber, uint8_t filenumber, uint8_t *data,
     if (m->friendlist[friendnumber].file_sending[filenumber].status != FILESTATUS_TRANSFERRING)
         return 0;
 
+    /* Prevent file sending from filling up the entire buffer preventing messages from being sent. */
+    if (crypto_num_free_sendqueue_slots(m->net_crypto, m->friendlist[friendnumber].crypt_connection_id) < MIN_SLOTS_FREE)
+        return 0;
+
     uint8_t packet[MAX_DATA_SIZE];
     packet[0] = filenumber;
     memcpy(packet + 1, data, length);
diff --git a/toxcore/net_crypto.c b/toxcore/net_crypto.c
index 9a840d11..14398c53 100644
--- a/toxcore/net_crypto.c
+++ b/toxcore/net_crypto.c
@@ -198,6 +198,17 @@ int read_cryptpacket(Net_Crypto *c, int crypt_connection_id, uint8_t *data)
     return -1;
 }
 
+/* returns the number of packet slots left in the sendbuffer.
+ * return 0 if failure.
+ */
+uint32_t crypto_num_free_sendqueue_slots(Net_Crypto *c, int crypt_connection_id)
+{
+    if (crypt_connection_id_not_valid(c, crypt_connection_id))
+        return 0;
+
+    return num_free_sendqueue_slots(c->lossless_udp, c->crypto_connections[crypt_connection_id].number);
+}
+
 /*  return 0 if data could not be put in packet queue.
  *  return 1 if data was put into the queue.
  */
@@ -579,9 +590,6 @@ int accept_crypto_inbound(Net_Crypto *c, int connection_id, uint8_t *public_key,
      * }
      */
 
-    /* Connection is accepted. */
-    confirm_connection(c->lossless_udp, connection_id);
-
     if (realloc_cryptoconnection(c, c->crypto_connections_length + 1) == -1
             || c->crypto_connections == NULL)
         return -1;
@@ -721,6 +729,8 @@ static void receive_crypto(Net_Crypto *c)
                                        c->crypto_connections[i].shared_key);
                     c->crypto_connections[i].status = CONN_ESTABLISHED;
                     c->crypto_connections[i].timeout = ~0;
+                    /* Connection is accepted. */
+                    confirm_connection(c->lossless_udp, c->crypto_connections[i].number);
                 } else {
                     /* This should not happen, timeout the connection if it does. */
                     c->crypto_connections[i].status = CONN_TIMED_OUT;
diff --git a/toxcore/net_crypto.h b/toxcore/net_crypto.h
index 5d21e4b6..0c1bffe6 100644
--- a/toxcore/net_crypto.h
+++ b/toxcore/net_crypto.h
@@ -121,6 +121,11 @@ void new_nonce(uint8_t *nonce);
  */
 int read_cryptpacket(Net_Crypto *c, int crypt_connection_id, uint8_t *data);
 
+/* returns the number of packet slots left in the sendbuffer.
+ * return 0 if failure.
+ */
+uint32_t crypto_num_free_sendqueue_slots(Net_Crypto *c, int crypt_connection_id);
+
 /*  return 0 if data could not be put in packet queue.
  *  return 1 if data was put into the queue.
  */